Wednesday, November 11, 2015

Using Let's Encrypt to Secure an Elastic Beanstalk Website

Since I've been pushing the library and academic publishing community to implement HTTPS on all their informations services, I was really curious to see how the new Let's Encrypt (LE) certificate authority is really working, with its "general availability" date imminent. My conclusion is that "general availability" will not mean "general usability" right away; its huge impact will take six months to a year to arrive. For now, it's really important for the community to put our developers to work on integrating Let's Encrypt into our digital infrastructure.

I decided to secure the website as my test example. It's still being developed, and it's not quite ready for use, so if I screwed up it would be no disaster. is hosted using Elastic Beanstalk (EB) on Amazon Web Services (AWS), which is a popular and modern way to build scaleable web services. The servers that Elastic Beanstalk spins up have to be completely configured in advance- you can't just log in and write some files. And EB does its best to keep servers serving. It's no small matter to shut down a server and run some temporary server, because EB will spin up another server to handle rerouted traffic. These characteristics of  Elastic Beanstalk exposed some of the present shortcomings and future strengths of the Let's Encrypt project.

Here's the mission statement of the project:
Let’s Encrypt is a free, automated, and open certificate authority (CA), run for the public’s benefit.
While most of us focus on the word "free", the more significant word here is "automated":
Automatic: Software running on a web server can interact with Let’s Encrypt to painlessly obtain a certificate, securely configure it for use, and automatically take care of renewal.
Note that the objective is not to make it painless for website administrators to obtain a certificate, but to enable software to get certificates. If the former is what you want, in the near term, then I strongly recommend that you spend some money with one of the established certificate authorities. You'll get a certificate that isn't limited to 90 days, as the LE certificates are, you can get a wildcard certificate, and you'll be following the manual procedure that your existing web server software expects you to be following.

The real payoff for Let's Encrypt will come when your web server applications start expecting you to use the LE methods of obtaining security certificates. Then, the chore of maintaining certificates for secure web servers will disappear, and things will just work. That's an outcome worth waiting for, and worth working towards today.

So here's how I got Let's Encrypt working with Elastic Beanstalk for

The key thing to understand here is that before Let's Encrypt can issue me a certificate, I have to prove to them that I really control the hostname that I'm requesting a certificate for. So the Let's Encrypt client has to be given access to a "privileged" port on the host machine designated by DNS for that hostname. Typically, that means I have to have root access to the server in question.

In the future, Amazon should integrate a Let's Encrypt client with their Beanstalk Apache server software so all this is automatic, but for now we have to use the Let's Encrypt "manual mode". In manual mode, the Let's Encrypt client generates a cryptographic "challenge/response", which then needs to be served from the root directory of the web server.

Even running Let's Encrypt in manual mode required some jumping through hoops. It won't run on Mac OSX. It doesn't yet support the flavor of Linux used by Elastic Beanstalk, so it does no good configuring Elastic Beanstalk to install it there. Instead I used the Let's Encrypt Docker container, which works nicely, and I ran a Docker-Machine inside "virtualbox" on my Mac.

Having configured Docker, I ran
docker run -it --rm -p 443:443 -p 80:80 --name letsencrypt \    
-v "/etc/letsencrypt:/etc/letsencrypt" \
-v "/var/lib/letsencrypt:/var/lib/letsencrypt" \ -a manual -d \
--server auth
(the --server option requires your domain to be whitelisted during the beta period.) After paging through some screens asking for my email address and permission to log my IP address, the client responded with
Make sure your web server displays the following content at before continuing:
To do this, I configured a virtual directory "/.well-known/acme-challenge/" in the Elastic Beanstalk console with a mapping to a "letsencrypt/" directory in my application (configuration page, software configuration section, static files section.). I then made a file named  "8wBDbWQIvFi2bmbBScuxg4aZcVbH9e3uNrkC4CutqVQ" with the specified content in my letsencrypt directory, committed the change with git, and deployed the application with the elastic beanstalk command line interface. After waiting for the deployment to succeed, I checked that responded correctly, and then hit <enter>. (Though the LE client tells you that the MIME type "text/plain" MUST be sent, elastic beanstalk sets no MIME header, which is allowed.)

IMPORTANT NOTES:  - Congratulations! Your certificate and chain have been saved at    /etc/letsencrypt/live/ Your cert    will expire on 2016-02-08. To obtain a new version of the    certificate in the future, simply run Let's Encrypt again.
...except since I was running Docker inside virtualbox on my Mac, I had to log into the docker machine and copy three files out of that directory (cert.pem, privkey.pem, and chain.pem). I put them in my local <.elasticbeanstalk> directory. (See this note for a better way to do this.)

The final step was to turn on HTTPS in elastic beanstalk. But before doing that, I had to upload the three files to my AWS Identity and Access Management Console. To do this, I needed to use the aws command line interface, configured with admin privileges. The command was
aws iam upload-server-certificate \ --server-certificate-name gitenberg-le \ --certificate-body file://<.elasticbeanstalk>/cert.pem \ --private-key file://<.elasticbeanstalk>/privkey.pem \ --certificate-chain file://<.elasticbeanstalk>/chain.pem
One more trip to the Elastic Beanstalk configuration console (network/load balancer section), and was on HTTPS.

Given that my sys-admin skills are rudimentary, the fact that I was able to get Let's Encrypt to work suggests that they've done a pretty good job of making the whole process simple. However, the documentation I needed was non-existent, apparently because the LE developers want to discourage the use of manual mode. Figuring things out required a lot of error-message googling. I hope this post makes it easier for people to get involved to improve that documentation or build support for Let's Encrypt into more server platforms.

(Also, given that my sys-admin skills are rudimentary, there are probably better ways to do what I did, so beware.)

If you use web server software developed by others, NOW is the time to register a feature request. If you are contracting for software or services that include web services, NOW is the time to add a Let's Encrypt requirement into your specifications and contracts. Let's Encrypt is ready for developers today, even if it's not quite ready for rank and file IT administrators.

Update (11/12/2015):
I was alerted to the fact that while was working, was failing authentication. So I went back and did it again, this time specifying both hostnames. I had to guess at the correct syntax. I also tested out the suggestion from the support forum to get the certificates saved in may mac's filesystem. (It's worth noting here that the community support forum is an essential and excellent resource for implementers.)

To get the multi-host certificate generated, I used the command:
docker run -it --rm -p 443:443 -p 80:80 --name letsencrypt \
-v "/Users/<my-mac-login>/letsencrypt/etc/letsencrypt:/etc/letsencrypt" \
-v "/Users/<my-mac-login>/letsencrypt/etc/letsencrypt/var/lib/letsencrypt:/var/lib/letsencrypt" \
-v "/Users/<my-mac-login>/letsencrypt/var/log/letsencrypt:/var/log/letsencrypt" \ -a manual \
-d -d \
--server auth
This time, I had to go through the challenge/response procedure twice, once for each hostname.

With the certs saved to my filesystem, the upload to AWS was easier:
aws iam upload-server-certificate \
--server-certificate-name gitenberg-both \
--certificate-body file:///Users/<my-mac-login>/letsencrypt/etc/letsencrypt/live/ \
--private-key file:///Users/<my-mac-login>/letsencrypt/etc/letsencrypt/live/ \
--certificate-chain file:///Users/<my-mac-login>/letsencrypt/etc/letsencrypt/live/
And now, traffic on both hostnames is secure!

Resources I used:

Update 12/6/2015:  Let's Encrypt is now in public beta, anyone can use it. I've added details about creating the virtual directory in response to a question on twitter.

Update 4/21/2016: When it came time for our second renewal, Paul Moss took a look at automating the process. If you're interested in doing this, read his notes.

Update 7/7/2016: Tony Gutierrez has an LE recipe for NodeJS on EB